This invention relates to a magnetic rotor bearing for suspending a rotor in a contact-free manner, in particular the rotor of an axial- or radial centrifugal blood pump, comprising a permanent- and electromagnet arrangement which stabilizes the position of, and suspends the rotor in a stator, in particular a housing, and comprising a circuit arrangement which is connected to at least one position sensor for the rotor, to adjust the magnetic field of the electromagnet arrangement.
Although the magnetic rotor bearing according to the present invention has been developed for the rotor of an axial- or radial-centrifugal blood pump of an artificial heart, the use thereof is in no way restricted to such centrifugal blood pumps. Instead, it is also suitable for a variety of rotors which may be mounted by means of a contact-free magnetic suspension. Thus, the magnetic rotor bearing method including the relevent circuit arrangement connected to one or more position sensors, for adjusting the magnetic force of the electromagnet arrangement provided therein is also suitable for mounting and driving gyroscopes, for example, for the use thereof in space technology, during flight operations and in submarines or the like, and for gyro-directional stabilizers which are provided, for example, in rocket-propelled missiles, and for direct-reading instruments or the like.
Even with respect to its use in pumps, the magnetic rotor bearing which is provided according to the present invention is not restricted to axial- or radial-centrifugal blood pumps, but it may also be used in other blood pumps which have a rotor which may be suspended magnetically. Furthermore, the magnetic rotor bearing may also be used in other rotor pumps. For example, it may be used for particular advantage in rotor pumps for radioactiveliquids, because if such rotor pumps are provided with a magnetic rotor bearing according to the present invention, they are free of friction and thus of maintenance since they do not require any mechanical bearings, valves or seals etc. which are subject to wear.
Magnetic rotor bearings for suspending a rotor in a contact-free manner are known in various embodiments. Thus, U.S. Pat. No. 3,938,913 discloses a flowing device for pumping and/or measuring the flow of agressive, radioactive or particularly pure flowing agents, in which apparatus a rotor is suspended in a contact free, magnetic manner in a housing. Electromagnets are provided in the housing for suspending the rotor, which magnetic form in each case a magnetic circuit with magnetic material which is positioned in the rotor opposite the electromagnets. Only attractive forces are used in these magnetic circuits by which the rotor is held, suspended, inside the housing.
However, the use of exclusively attractive forces which are produced with electromagnetics suffers from considerable disadvantages:
(a) The stability of the magnetic bearing, i.e., the stability in the maintenance of the correct suspended position of the rotor, in which the rotor is positioned at an approximately equal distance in all radial directions from the inside wall of the housing, is most unsatisfactory with respect to self- and independently excited oscillations. A magnetic rotor bearing of this type tends towards oscillation relatively easily on account of the delayed built-up of the magnetic field. This delayed magnetic field build-up is a result of the relatively great inductances which are necessary to build up the complete magnetic field in each case by electric currents, and, because of the high permeability of iron (.mu. relative up to 10,000), high absolute inductances are produced which result in a delayed increase in the current.
(b) The energy consumption of such a magnetic rotor bearing having electromagnets is very high, and at the same time the efficiency is relatively poor, so that undesired thermal energy is produced to a considerable extent which is not only wasted and the dissipation of which is not only difficult, but is also extremely dangerous in the case of blood pumps, because blood albumen coagulates at 42.degree. C.
(c) The specific forces are relatively low, as are the relative peak forces, because iron has a high density and fields which are essentially above 10 kilogauss produce saturation phenomena, .mu. relative approaching 1.
Furthermore, published European Application No. 0,060,569 or European Patent Application No. 82 102 188.8, disclose a magnetic rotor bearing which was previously developed, inter alia, by the inventors of the present magnetic rotor bearing, for suspending a rotor of a centrifugal blood pump in a contact-free manner. In that bearing, a combined electromagnet- and permanent magnetic arrangement is provided for suspending the rotor, which arrangement consists of electromagnets which are provided in the stator forming the housing of the centrifugal blood pump, and consists of permanent magnets which are positioned in the rotor opposite the electromagnets, so that they co-operate with the electromagnets.
This combined electromagnet- and permanent magnet arrangement basically suffers from the same disadvantages as have been mentioned above in connection with the magnetic rotor bearing according to U.S. Pat. No. 3,938,913. The exclusive use of electromagnets in the stator leads to a relatively high energy consumption and thus to a considerable generation of heat, and moreover, a relatively unsatisfactory stability results on account of the delayed field build-up which is inherent to electromagnets.